The present invention relates to a new and improved construction of a power take-off gearing or gear unit intended to be installed at a drive or propulsion system of a marine vessel.
Generally speaking, with the arrangement of the invention a propeller shaft is flanged to the power take-off shaft of a main engine or gearing and there is arranged coaxially to the propeller shaft, within a housing, a large gear of the power take-off gearing or gear unit which is driven by the propeller shaft. The housing is supported as a self-contained unit at the ship's foundation.
Such power take-off gearing or gear units, also referred to in the art as PTO-gearing, are used with vessels for the purpose of driving auxiliary current generators for pumps, lifting devices and other equipment. For such fields of application there are required drive capacities or outputs, in the order of 250 to 2500 kW, corresponding to approximately one-tenth of the main engine output. Since pumps, lifting devices and so forth also must be capable of being operated when the vessel is in the harbor, there are operatively associated with the auxiliary current generators separate engines, generally high-speed diesel engines. When the vessel or ship is at sea it is however more economical to drive all of the generators from the ship's engine, which generally is a slow-running diesel engine, which in contrast to the high-speed engines can be operated with comparatively less expensive bunker fuel, and additionally, has a lower specific fuel consumption, usually also develops less noise.
Because of these advantages not only are new ship constructions equipped with such power take-off gear units, but also older ship constructions are increasingly equipped with the same. The retrofitting of existing power take-off gearing requires, however, expensive modifications of parts of the existing propulsion system or drive of the vessel or ship.
Thus, for instance from the publications LuS-Mitteilungen 72 I/78 and Renk Technik Information 15, there have become known in this technology power take-off gearing or gear units of the previously described type, wherein the large gear of the power take-off gear unit is relatively fixedly secured to a shaft portion of the propeller shaft. This shaft portion or piece is flanged, for instance bolted, to the power take-off shaft of the main engine or gearing. The housing of the power take-off gearing is mounted at both ends of the large gear arranged therein upon the shaft portion of the propeller shaft and is moveably supported at the ship's foundation in such a manner that the entire power take-off gearing can perform radial movements, especially can follow bending vibrations of the shaft portion of the propeller shaft which is enclosed by the power take-off gearing. This design presupposes that the shaft portion of the propeller shaft, which is enclosed by the housing of the power take-off gearing, is especially constructed for the attachment of the large gear and for the mounting of the housing of the power take-off gearing. In order to retrofit a power take-off gear unit it is therefore necessary to exchange a shaft portion or piece of the propeller shaft or at least to provide such with attachment surfaces for the large gear as well as with bearing surfaces for the housing of the power take-off gearing or gear unit. These operations cannot be carried out on-board a ship. During operation of the heretofore known constructions of power take-off gear units difficulties can arise by virtue of the fact that the quite considerable sluggish mass of the power take-off gearing can be placed into movement by bending vibrations of the shaft portion of the propeller shaft which is enclosed by the power take-off gearing. Consequently, there are produced appreciable mass inertia forces which, on the one hand, intensively load the propeller shaft as well as its bearing and, on the other hand, the bearings with which the power take-off gearing is mounted upon the propeller shaft.
In German Pat. No. 2,501,675 there is also disclosed a marine vessel gearing or gear unit wherein a speed reduction gearing and a power take-off gearing arranged between the speed reduction gearing and the ship's engine form a structural unit. The power take-off gearing is provided with a housing which is directly mounted at the housing of the speed reduction gearing. Mounted within the housing of the power take-off gearing is a hollow hub of a large gear through which piercingly extends a torsion shaft which interconnects the ship's engine with the speed reduction gearing. The large gear of the power take-off gearing is connected by a double tooth clutch with a flange formed at the torsion shaft. A clutch or coupling sleeve constituting part of the double tooth clutch in turn encloses with radial play the torsion shaft, and also extends with radial play through the hollow hub of the large gear of the power take-off gearing. This clutch or coupling sleeve is provided at both ends with a respective ring of external teeth. One of both rings of these external teeth, i.e. the external gears, engages with a ring of internal teeth or an internal gear which is formed at a first clutch ring which is bolted to the aforementioned flange of the torsion shaft. The other external teeth of the clutch sleeve engages with an internal ring of teeth of a second clutch ring which is bolted with the hub of the large gear of the power take-off gearing at its side facing away from the first clutch ring. This state-of-the-art arrangement of a power take-off gearing between a ship's engine and the related speed reduction gearing is only suitable for use in those situations where the speed reduction gearing and the power take-off gearing form a self-contained unit right from the start; retrofitting of the power take-off gearing at an existing propulsion system or drive of a ship cannot be carried out without disassembly and modification of the speed reduction gearing.